Field of the Invention
The invention relates to a device for generating an atmospheric plasma beam for treating the surface of a workpiece having a plasma beam which rotates about an axis and produces a wide treatment path when moving over the surface. The invention also relates to an apparatus having at least one plasma device which rotates about an axis and in this process generates at least one plasma beam in a circular movement over the surface. A wide treatment path is also produced when the at least one plasma beam moves over the surface. In addition, the invention relates to a method for treating the surface of a workpiece using such a device or such an arrangement.
Description of Related Art
Within the scope of this description, a treatment of a surface with a plasma beam is in particular understood to encompass a surface pretreatment, by means of which the surface tension is altered and a better wettability of the surface with fluids is obtained. A treatment of the surface can also be understood as a surface coating, in which by adding at least one precursor to the plasma beam a surface coating is obtained by a chemical reaction which takes place in the plasma beam and/or on the surface of the workpiece, wherein at least a part of the chemical products is deposited. In addition, a surface treatment can also mean cleaning, disinfection or sterilisation of the surface.
A device for generating an atmospheric plasma beam for treating the surface of a workpiece having a plasma beam rotating about an axis is known from EP 1 067 829 B1. This device has on a tubular housing, which has an axis A, an inner electrode which is arranged within the housing and which preferably runs parallel to the axis A or which in particular is arranged in the axis A. During operation of the device, an electric voltage is applied to the inner electrode by means of which voltage an electric discharge occurs which by interaction with the working gas flowing within the housing generates a plasma. The plasma together with the working gas is transported further.
In addition, the device has a nozzle arrangement having a nozzle opening for discharging a plasma beam to be generated in the housing, wherein the nozzle arrangement is preferably arranged at the end of the discharge path, is earthed and channels the emanating gas and plasma beam. The direction of the nozzle opening runs at an angle relative to the axis A, wherein the direction of the nozzle opening can be assumed parallel to the central direction of the emanating plasma beam and can be defined, for example, parallel to the normal of the opening. For this purpose, a channel runs in the shape of an arc within the nozzle arrangement, in order to divert the gas and plasma beam starting from inside the housing. Finally, the nozzle arrangement is rotatable relatively about the axis A, wherein the nozzle arrangement is either rotatable with respect to the housing and the inner electrode or is connected to the housing in a torque proof manner while the housing rotates relative to the inner electrode. The nozzle arrangement or the nozzle arrangement and the housing are driven by a motor for the rotational movement.
An apparatus for treating a surface with atmospheric plasma is known from EP 0 986 939 B1 and has two devices for generating an atmospheric plasma beam, wherein each of the two devices has a tubular housing, which has an axis A or A′, respectively, an inner electrode arranged within the housing and a nozzle arrangement having a nozzle opening for discharging a plasma beam to be generated in the housing, wherein the two devices are connected together rotatable about a common axis B, and wherein a drive is provided for generating a rotational movement of the devices about the axis (B).
Using the two previously described devices or apparatuses, it is possible to produce a relatively wide treatment path by moving the rotating plasma beams along the surface of the workpiece to be processed. Therefore, these techniques are used a great deal.
Even if a plurality of paths of plasma treatment of the surface parallel and partly overlapping result in larger areas being able to be plasma treated, differences in the intensity of the plasma treatment on the surface occur transverse to the direction of movement of the device or apparatus. This effect is explained in more detail with the aid of FIG. 1.
The treatment path of a plasma beam of an above described device is illustrated in FIG. 1a, wherein the trajectory (line) represents the point of impact of the maximum plasma intensity. The device is moved in the y direction i.e. upwards in FIG. 1, in order to apply the rotating plasma beam continuously over a strip with an approximate width dx and treat the surface with plasma. The direction of movement (y) causes the outer areas of the treatment path (dx) to be more intensively treated with the plasma in the area of the dashed lines than is the case for the middle areas of the treatment path.
This results in the intensity distribution illustrated in FIG. 1b, which has two maxima which occur in the outer areas of the treatment path, indicated by the dashed lines. In between, only a distinctly low intensity of plasma treatment takes place, so that a minimum intensity occurs in the middle of the treatment path.
For this reason, the surface is but inadequately plasma treated and moreover insufficiently plasma treated in regular strips. Therefore, the speed of movement of the device relative to the surface has to be regularly slowed down, so that saturation of the plasma treatment is also achieved in the middle areas of the treatment path. The application of the device is as a consequence constrained.